Priority rights based upon Japanese Application No. 104172/2000, filed Feb. 28, 2000, are claimed under 35 U.S.C. xc2xa7119.
The present invention relates to a novel carnosic acid derivatives for promoting the synthesis of nerve growth factor, more particularly, a carnosic acid derivative capable of efficiently promoting the synthesis of nerve growth factor in the treatment of nerve-denaturing diseases such as Alzheimer-type dementia and brain ischemia pathologies. The present invention also relates to a composition comprising the carnosic acid derivative as well as a method of promoting the synthesis of nerve growth factor.
Senile dementia has a tendency to increase with the shift to an aging society. This tendency has become an extremely large social problem. A number of diseases are known which are responsible for senile dementia. They are roughly divided into dementia attributable to an organic disorder of the brain, dementia incidental to a disease of other organs than the brain, and dementia attributable to a physical disease due to stress. In particular, the dementia attributable to an organic disorder of the brain, which constitutes a greater part of the causes of dementia, is divided into cerebrovascular dementia and Alzheimer-type dementia due to the differences of the causes.
Currently, it has been known that a drug such as a cerebrovascular dilator exhibits a certain effect on the cerebrovascular dementia. However, the causes of development of Alzheimer-type dementia are not known yet, and a pharmacotherapy and other treating methods suitable for preventing the development and progression of the dementia are not known yet. Accordingly, it is greatly desired to develop a drug useful for the treatment of dementia due to an organic disorder of the brain, in particular, Alzheimer-type dementia.
Recently, it has been found that a neurotrophic factor such as nerve growth factor (NGF) secreted from nerve cells has an excellent effect on nerve-denaturing diseases, and special attention has been paid to the factor. NGF is a factor necessary and important to the growth and functional maintenance of the nervous tissue. NGF is essential formaturation, differentiation and survival of sensory and sympathetic nerves in the peripheral nervous system as well as for those of large cell cholinergic neurons in the central nervous system. Also, NGF exhibits an effect of preventing denaturing of nerve cells when undergoing a brain lesion. Accordingly, it is believed that an elevation of the NGF level in the living body is effective for treating a disorder of central functions (including Alzheimer-type dementia and cerebrovascular dementia), a lesion of peripheral nerves, a diabetic neuropathy and a disorder of peripheral functions (including amyotrophic lateral sclerosis).
However, NGF is a protein having a high molecular weight of about 13,000 in its monomer form and about 26,000 in its dimer form, and can not pass through the blood-brain barrier. Accordingly, it is necessary to administer NGF intraventricularly, for example, when the treatment of a disorder of central functions is aimed. In addition, it is difficult to prepare NGF in a large amount. Thus, it is very problematic to use NGF per se. Consequently, it is very difficult to use NGF per se clinically.
A method of administering a substance for promoting the synthesis of NGF in the living body, instead of NGF, is also known in the art. For example, Y. Furukawa et al. (FEBS Lett., Vol.208 (1986), p.258 et seq.) discloses that catecholamines (epinephrine, norepinephrine and dopamine) are used as the substance for promoting the synthesis of NGF.
However, they are hormone substances, and therefore, the administration of them causes a problem of losing a quantitative balance of hormones in the living body.
The present invention is addressed to the solution of the above problems.
Thus, the object of the present invention is to provide a substance capable of promoting an effective synthesis of NGF in the living body.
Another object of the present invention is to provide a composition for promoting the synthesis of NGF in the living body.
Other object of the present invention is to provide a method of promoting the synthesis of NGF in the living body.
The present inventors have intensively searched for a substance having a potent effect of promoting the synthesis of NGF. As a result, they found that carnosic acid derivatives of the following formula (I) have such an effect: 
wherein R1 is a hydrogen atom or a C1-C5 alkyl group, and R2 and R3 independently of one another are a hydrogen atom, a C1-C5 alkyl group or a C1-C5 acyl group,
provided that at least one of R1, R2 and R3 is not a hydrogen atom.
Thus, the present invention provides a carnosic acid derivative of the above formula (I).
Also, the present invention provides a composition for promoting the synthesis of nerve growth factor comprising a carnosic acid derivative of the above formula (I) as an effective ingredient.
Furthermore, the present invention provides a method of promoting the synthesis of nerve growth factor comprising administering an effective amount of a carnosic acid derivative of the above formula (I) as an effective ingredient to a subject requiring such promotion.
A preferred carnosic acid derivative is a compound of the above formula (I) wherein R1 is a hydrogen atom, and both R2 and R3 are acetyl groups.
Another preferred carnosic acid derivative is a compound of the above formula (I) wherein R1 is a methyl group, and both R2 and R3 are hydrogen atoms.
The present invention is described in more detail in the following.
The present carnosic acid derivatives of the above formula (I) may be prepared by chemically modifying carnosic acid of the following formula (II): 
Although carnosic acid of the above formula (II) may be prepared by chemical synthesis, it is advantageous to obtain it by extraction from a plant containing carnosic acid, for example, from rosemary (Rosmarinus officinalis L.) or sage (Salvia officinalis L.).
For example, rosemary or sage may be extracted in the following manner. Firstly, the whole plant, leaves and/or petals of rosemary or sage are soaked in ethanol or an aqueous ethanol solution having an ethanol concentration of 80% (v/v) to 100% (v/v) to obtain an extract. Typical extraction conditions include a temperature of about 0xc2x0 C. to about 50xc2x0 C. and an extraction time of about one hour to about 48 hrs.
Then, water is added to the extract so as to give an ethanol concentration of not greater than 40% (v/v). By doing so, it is possible to deposit a precipitate containing carnosic acid from the extract. Alternatively, the above extract may be concentrated to one-half to one-twentieth of its original volume, and then, water may be added to the concentrate to deposit a precipitate containing carnosic acid. Typical deposition conditions include a temperature of about 0xc2x0 C. to about 25xc2x0 C. and a deposition time of about one hour to about 48 hrs.
By repeating several times the step of adding ethanol or water to the extract so as to give a particular ethanol concentration, the step of dissolving or depositing a precipitate, and the step of filtration, it is possible to obtain a precipitate containing carnosic acid of the formula (II) in a large amount.
Subsequently, carnosic acid of the formula (II) can be obtained by removing impurities from the precipitate through various column chromatographic means. Those skilled in the art can easily identify by well known means such as 1H-NMR or 13C-NMR that the substance thus obtained is carnosic acid of the formula (II).
The present carnosic acid derivatives of the above formula (I) may be prepared from the carnosic acid in the following manner.
Thus, the derivatives of the above formula (I), wherein R1 is a C1-C5 alkyl group, may be prepared by a known esterification method in the art. For example, they may be prepared by reacting carnosic acid with an alcohol such as methanol, ethanol, propanol, butanol or pentanol in the presence of an acid such as hydrogen chloride, sulfuric acid or p-toluenesulfonic acid. Alternatively, the methyl-esterified derivative may be prepared by using a diazomethane ether solution.
The derivatives of the above formula (I), wherein R2 and R3 are C1-C5 acyl groups, may be prepared by reacting carnosic acid with an appropriate acid anhydride or acid halide in the presence of a base such as triethylamine or pyridine.
The derivatives of the above formula (I), wherein R1, R2and R3 are C1-C5 alkyl groups, may be prepared by reacting carnosic acid with an appropriate alkyl halide in the presence of a base such as sodium hydride or sodium amide.
The above reaction may be carried out in an appropriate solvent. Examples of the solvent include chloroform, diisopropyl ether, acetone, methyl ethyl ketone, dioxane, dichloromethane, diethyl ether, tetrahydrofuran, toluene, benzene, xylene, n-hexane and heptane.
If it is necessary to prepare the derivatives of the above formula (I) wherein R1 is a hydrogen atom, and R2 and R3 are C1-C5 alkyl groups, the derivatives of the above formula (I), wherein R1, R2 and R3 are C1-C5 alkyl groups, may be hydrolyzed by using an aqueous alkali solution such as an aqueous sodium hydroxide or potassium hydroxide solution.
The present composition for promoting the synthesis of nerve growth factor comprises a carnosic acid derivative of the above formula (I) as an effective ingredient. The content of the above derivative contained in the composition is preferably about 0.00001% by weight to less than 100% by weight, more preferably about 0.001% by weight to less than 100% by weight, per 100% by weight of the composition. If the content of the derivative is less than 0.00001% by weight, the composition can not promote the production of NGF sufficiently.
The carnosic acid derivatives of the above formula (I) may be made up into suitable forms such as food or drug compositions. Also, the compositions according to the present invention may be used for both of oral administration and parenteral administration.
In case of making up into food compositions, the above derivatives are mixed with suitable materials which may be commonly used as food materials. Examples of the food materials are rice, wheat, corn, potato, sweet potato, soybean, sea tangle, wakame (Undaria pinnatifida), agar weed; starch syrup; sugars such as lactose, glucose, fructose, sucrose, mannitol; and combinations of these materials. In addition, flavoring agents, coloring agents, sweetening agents, edible oils, vitamins and the like may be added to the food compositions. These materials and additives may be used alone or in combination with one another. Also, the food compositions may be made up into a desired shape, if necessary, by adding water.
In case of making up into drug compositions, the above derivatives are mixed with suitable additives. Examples of the additives are surfactants, excipients, coloring agents, preservatives, coating aids and combinations of these additives. These additives may be those commonly used in the production of drug compositions and are not limited to particular ones. More specific examples of the additives are lactose, dextrin, sucrose, mannitol, corn starch, sorbitol, crystalline cellulose, polyvinylpyrrolidone and combinations of these additives. Also, flavoring agents, sweetening agents and the like may be added to the drug compositions. In addition, other drugs may be added to the drug compositions, if necessary.
There is no limitation in dosage forms of the drug compositions and they may be produced in suitable dosage forms according to a conventional process. For oral administration, in particular, the compositions may be prepared in the forms of capsules, tablets, powder, slow-releasing agents and the like. For parenteral administration, the compositions may be prepared in the forms of injections, infusions and the like.
There is no limitation in the content of the above suitable materials and additives, and they may be used depending on the content of the carnosic acid derivatives of the above formula (I).